The present invention relates to techniques for changing or controlling a sound (i.e., musical sound or tone) of an acoustic piano.
In the field of acoustic pianos, there have been developed control techniques for changing a sound generated by a keyboard performance on the piano. One example of such control techniques additionally uses an electronic sound generator that outputs an electronic audio signal, such as that of a desired musical instrument sound, in accordance with behavior of a key. In such a case, an electric sound etc. are generated from the electronic sound generator together with an acoustic sound generated from the acoustic piano, or without such an acoustic sound (i.e., with the acoustic piano kept in a silent state). However, with the control technique where an electric sound generated from the electronic sound generator is directly inserted as noted above, a natural feeling of sound generation by the acoustic piano sometimes cannot be reproduced, so that it has heretofore been desired to impart an acoustic piano sound with an acoustic effect having a natural feeling.
Japanese Patent Application Laid-open Publication No. HEI 05-73039 (hereinafter referred to as “the relevant patent literature”) discloses a technique which, for imparting an acoustic effect having a natural feeling while maintaining a natural acoustic piano sound, extracts, as a string vibration signal, vibration of a string in real time when the acoustic piano is generating a sound through the vibration of the string, then generates a soundboard driving signal by performing arithmetic operations for imparting a desired acoustic effect to the extracted string vibration signal and then actively vibrates the soundboard with the generated soundboard driving signal. With the technique disclosed in the relevant patent literature, the soundboard driven with the soundboard driving signal vibrates, in response to the soundboard driving signal, just like a speaker cone and can thereby impart an acoustic effect having a natural feeling. However, because the vibration signal to be used for driving the soundboard is merely a signal obtained by picking up the vibration of the string of the acoustic piano as-is, it comprises various frequency components, and thus, the technique disclosed in the relevant patent literature cannot perform free control, like control for driving the soundboard while emphasizing a particular harmonic component, so that it can achieve only poor control performance or controllability.
Also note that, in the aforementioned type of soundboard driving construction, vibration of the soundboard produced by the soundboard driving signal containing various frequency components is fed back to the string being vibrated by striking with a hammer. With the technique disclosed in the relevant patent literature, where such feedback vibration to the string contains various and complicated frequency components, an unintended sound generation state may sometimes result due to synthesis between the original string vibration and the feedback vibration depending on relationship between the original string vibration and the feedback vibration. As a consequence, a resultant piano sound having been imparted with an acoustic effect may sometimes end up having a reduced natural feeling of the acoustic piano despite a user's intention.